Wells that pump natural gas from the ground in Colorado have leaked about twice as much gas into the atmosphere as previously thought, a new study finds.
That could tarnish gas’s image as clean source of energy. Natural gas, made mostly of methane, does give off less carbon dioxide than coal when burned. But methane itself strongly warms the atmosphere, which means even relatively small releases can have a big impact on the climate.
“We’re seeing raw natural gas in the atmosphere,” says Gabrielle Pétron, an atmospheric scientist at the National Oceanic and Atmospheric Administration and the University of Colorado Boulder. Her team reports the new findings, based on data gathered in 2007 and 2008, in an upcoming issue of the Journal of Geophysical Research.
Pétron and her colleagues monitored air quality near Denver using a 300-meter tower. NOAA maintains a network of such towers across the country. This one lies southwest of the Denver-Julesburg Basin, an area that feeds more than 20,000 natural gas wells.
When winds blew in from the basin, levels of methane detected by sensors on the tower spiked. Landfills, cattle feedlots and wastewater treatment plants probably belched some of the gas into the sky. But methane from gas wells was accompanied by other components that allowed it to be fingerprinted and separated out in the analysis.
These measurements suggested that about 4 percent of the methane in the gas wells was leaking. Previous studies by the Environmental Protection Agency and by industry groups pegged this loss at between 1 and 2 percent. But the earlier estimates were done by measuring leakages from individual pieces of equipment.
“You tend to underestimate things when you do that kind of bottom-up approach,” says Robert Howarth, a biogeochemist at Cornell University.
Last year, Howarth found higher-than-expected levels of methane being released from wells that extract gas from shale — a process called hydraulic fracturing, or fracking. His estimates, reported in 2011 in Climatic Change, suggested that extracting shale gas is substantially worse for climate change than mining coal.
Pétron hasn’t made this comparison. Her main concern, she says, is to work with the gas industry to keep methane out of the air.
Kathleen Sgamma of the Western Energy Alliance in Denver says gas wells in the area have already made some changes since the data used in the new study were collected that should cut down on leakage.